The U.S. military is planning a new drone base in Africa that would expand its surveillance of al-Qaeda fighters and other militants in northern Mali, a development that would escalate American involvement in a fast-spreading conflict.

A U.S. defense official called the plan “preliminary” and said the Pentagon, the State Department, the White House and the government of Niger would all have to approve. “But it would be a good place to be, in terms of access,” the official added.

If approved, the plan would fill a gap in the Pentagon’s military capabilities over the Sahara, which remains beyond the reach of its drone bases in East Africa and southern Europe. U.S. officials said the plan was to use the Predators strictly for surveillance missions, not airstrikes, but they acknowledged that the drones could easily be armed if circumstances changed.

The U.S. military has been flying a handful of small turboprop surveillance planes over northern Mali and West Africa for years, but the PC-12 aircraft are limited in range and lack the sophisticated sensors that Predators carry.

Some senior U.S. officials have also worried that the PC-12 aircraft could be shot down by militants with a shoulder-fired missile. The U.S. ambassador to Mali, Mary Beth Leonard, suspended the flights over Mali last year because of concerns that a pilot or crew could be held hostage if forced to make an emergency landing, according to two U.S. officials who spoke on the condition of anonymity.

The PC-12 turboprops have been largely based in Burkina Faso, a small West African country that shares a long border with Mali. One option under consideration at the Pentagon would be to deploy drones to Burkina Faso as well, possibly at a military base in Ouagadougou, the capital.

But Niger has been gaining favor since last year, when the U.S. military relocated one of the PC-12 turboprop planes to the capital, Niamey, after reaching an agreement with Niger officials, according to a current and a former U.S. official familiar with the operation. The United States also won permission for the surveillance aircraft to refuel in the northern city of Agadez, the officials said.

Army Gen. Carter F. Ham, the chief of the U.S. military’s Africa Command, visited Niger this month to discuss expanding the military relationship between the two countries, U.S. officials said.

Deploying unmanned Predators to the region would eliminate the risk of crew capture in the event of a shoot-down or accident, but it would also greatly increase the number of U.S. troops on the ground. A Predator base could require as many as 250 Air Force personnel to launch and maintain the drones, as well as to provide protection for U.S. troops.

“You’ve just upped the ante,” said the former U.S. official, who worked on counterterrorism programs in West Africa and said the idea of moving Predators to the region has been discussed for two years. “You’ve militarized the problem.”

In recent days, the United States and Niger have finalized a new “status of forces” agreement that would permit the expanded presence of U.S. troops in the country.

The Obama administration has increased counterterrorism assistance to Niger in recent years and sent Special Forces personnel there on training missions, but the numbers have been limited to a dozen or so troops at a time.

The Pentagon has been hamstrung in its effort to gain better intelligence about the growing number of al-Qaeda fighters and other extremists in the Sahara because of a lack of bases in the region, but also because of legal restrictions on what it can do on Malian territory.

The Obama administration withdrew trainers and shut off military aid to Mali in March after a coup there toppled a democratically elected government. U.S. officials cannot resume military assistance to Mali until it holds new elections — a far-fetched prospect, given the political turmoil there.

U.S. officials said they were facing a balancing act over the need to improve their intelligence collection amid a reluctance to send more aircraft or troops to the region.

“With Niger, the first question is, is this something they’re willing to host?” said a senior U.S. official who spoke on the condition of anonymity to discuss internal planning. “If the answer is yes, then the question is, can you accomplish something like that with an acceptable footprint?”

As a condition of winning permission for a drone base, the U.S. government might be required to share intelligence from the flights with the Niger military — an added complication that has scuttled or limited other partnerships in the region, U.S. officials said.­­